WGSL spec only allows xyzw and rgba swizzle components. GLSL-only
s/t/p/q components were incorrectly accepted. Additionally, mixing
namespaces (e.g., v.xg combining xyzw with rgba) was not rejected.

Matches Rust naga Components::new() which validates all characters
belong to the same namespace (xyzw or rgba).

BUG-WGSL-004: reject stpq swizzle
BUG-WGSL-008: reject mixed swizzle namespace

@compute entry points without @workgroup_size were silently accepted,
defaulting to [1,1,1]. WGSL spec requires @workgroup_size to be
explicitly present on compute shader entry points.

Matches Rust naga: Error::MissingWorkgroupSize.

BUG-WGSL-003

array<f32, 0> was silently accepted. WGSL spec requires array size
to be a positive integer. Now returns a clear error message.

BUG-WGSL-007

Previously const_assert was parsed but treated as a no-op during
lowering. Now const_assert expressions are evaluated at both module
and function scope, matching Rust naga's ConstAssertFailed / NotBool
behavior.

Supports bool literals, negation (!), logical operators (&&, ||),
comparison operators (==, !=, <, <=, >, >=), and named constants.

WGSL spec requires both @binding and @group on resource variables.
Previously @binding(0) without @group compiled silently. Now the
lowerer validates that both attributes are present and reports a
clear error when one is missing.

Functions marked with @must_use now produce an error when their
return value is discarded as a statement (e.g. foo();). The result
must be used in an assignment, return, expression, or phony (_ =).
Matches Rust naga's FunctionMustUseUnused validation.

Complex const_assert expressions (select(), all(), float comparisons)
are silently accepted when they cannot be evaluated by the simple
constant evaluator. This prevents regressions on valid shaders like
const_assert.wgsl and select.wgsl while still catching the common
case of const_assert false.

…parity verified